Vertical high-speed rotating disk reactors, in which the gas or gases are injected downwardly onto a substrate surface rotating within a reactor, are frequently employed for metal organic chemical vapor deposition (MOCVD). Vertical disk-type CVD reactors, in particular, have been found useful for wide varieties of epitaxial compounds, including various combinations of semiconductor single films and multilayered structures such as lasers and LED'S. In these reactors, one or more injectors spaced above a substrate carrier provide a predetermined gas flow, which upon contact with the substrate, deposits layers of epitaxial material on the surface of the substrate.
For larger wafers, rotating disk reactors employ several injectors spaced above the substrate. The injectors are typically spaced above the wafer in various positions along one or more radial axes of the wafer, relative to the central axis of the substrate carrier. Frequently, the rate of source reactant material injected into the reactor varies from injector to injector to permit the same molar quantity of reactant to reach the surface of the substrate. Hence, some reactant injectors may have different gas velocities than others. This variation in reactant velocity is, in pertinent part, due to the relative placement of the injectors. As the reactor carrier holding the substrate rotates at a predetermined rate, the injectors near the outer edge of the carrier cover a larger region of surface area on the carrier than the injectors closer to the center of the carrier in any given time period. Thus, the outer injectors typically employ a greater gas velocity of reactant than the inner injectors in order to maintain desired uniformity. For example, individual injector gas velocities may differ by a factor of as much as three to four between adjacent injectors.
While this variation in gas velocity helps to ensure a more uniform layer thickness, it may also cause turbulence between the injector flows due to their varying velocities. Also, the risk of side effects such as uneven layer thickness, dissipation of reactant, or premature condensation of reactant may be increased.